Transmenu powered by JoomlArt.com - Mambo Joomla Professional Templates Club

The main objective of the QCDnet is fostering the interchange of ideas and methods in non-perturbative QCD and their applications to hadron phenomenology, including also few- and many-hadron systems. This is intimately linked to the on-going experimental efforts at COMPASS (CERN), COSY (Jülich), DAPHNE (Frascati), ELSA (Bonn), GSI (Darmstadt) and MAMI (Mainz) for light quark systems and at BaBaR (SLAC), BELLE (KEK), BES (Beijing) and CLEO (Cornell) for heavy and heavy-light systems. QCDnet is expected to achieve large synergetic effects by coordinating the efforts of analysing data based on various probes (electromagnetic, hadronic) and at different energies (from various thresholds through the resonance region of QCD to the heavy quark regime). In addition, techniques based on effective field theories are to be developed to further refine the results obtained from lattice simulations in the realm of strong QCD. Furthermore, nuclei are fine laboratories for certain aspects of hadron structure and interactions as well as for tests of QCD symmetries and are therefore also included in the network.

A second objective is to prepare methods to make best use of the upcoming FAIR facility at Darmstadt. In particular, the experience gained in dealing with light quark systems will be extended into the charm quark sector, which allows one to investigate the transition from strong to perturbative QCD. In addition, heavy quark decays (charm and bottom) allow for many stringent tests of strong QCD through final state interactions in hadronic and radiative decays. A re-occurring theme will be to investigate the structure of the observed hadrons and trying to unravel their true nature (conventional 3-quark or quark-antiquark states, hadronic molecules, multi-quark states, etc.). Again, theoretical tools will be developed to make such identifications possible and unambiguous.

The physics issues pertinent to QCDnet can be grouped into four majors subtopics (institutions involved in the various tasks are shown in parenthesis):

1.      Hadron dynamics with light quarks will focus on the structure and dynamics of QCD for systems with the light up, down and strange quarks. In these systems, the spontaneously and explicitly broken chiral symmetry of QCD plays a prominent role as its consequences can be analyzed to high precision utilizing chiral perturbation theory (CPHT), the effective field theory (EFT) of the Standard Model at low energies (Bonn, Coimbra, Tübingen, Madrid, Valencia, Darmstadt, Lund, Graz, Bochum, Manchester, Bern, Marseille, Mainz, Ankara). CPHT can also be used in reactions involving baryons, in particular the ground-state octet and the low-lying decuplet. Chiral symmetry puts severe constraints on the interactions of mesons (Salamanca, Lund, Bern, Marseille, Moscow, Ankara) and baryons (Bonn, Graz, Bochum, Manchester, Lisbon, Paris, Ankara) and these structures will be further explored using new data on various hadron decays and reactions from CERN, DAPHNE, MAMI and other laboratories. Furthermore, going to the regime of excited mesons and baryons, further quark model studies (Bonn, Pavia, Tübingen, Madrid, Graz, Helsinki, Lisbon) combined eventually with coupled channel dynamics to incorporate the strong final-state interactions (Graz, Jülich, Krakow, Murcia, Barcelona, Helsinki, Paris) will be performed, flanked by studies of hadronic molecules (Jülich, München, Valencia, Darmstadt) and unitary extensions of chiral perturbation theory to unravel the physics behind the bound states of QCD. Last but not least, the connection of strong QCD to hard perturbative processes will be investigated through models for generalized parton distributions and structure functions (Pavia, Tübingen, Bochum, Moscow).

2.      Hadron dynamics with heavy quarks will focus in particular on the interplay of light and heavy quark systems by combining appropriate effective field theories, like e.g. heavy quark EFT and CPHT. In addition, final-state interactions in decays of heavy quark systems give important information on light quark dynamics such as the scalar meson form factors in J/ψ → VPP or B → 3P decays (Salamanca, Coimbra, Murcia, Darmstadt, Bonn). Similarly, scalar meson mixing can be studied very precisely in J/ψ → φπη decays. Also, J/ψ and B decays into baryon-antibaryon pairs give very detailed information on baryon-antibaryon interactions not easily accessible in other reactions and can also be used to further analyse the nucleon electromagnetic form factors in the time-like region (Salamanca, Coimbra, Bern, Mainz). All this is intertwined with the calculation of long-distance effects of strong interaction corrections to weak decays (Jülich, Marseille), which need to be sharpened to improve the precision of Standard Model tests through the CKM unitarity. One of the central issues of this subproject will be to unravel the nature of the D_s(2317) and (2460) mesons as well as the exotic charmonium states like the X(3872), the Y(3940), the Z(3930) etc., by systematically confronting (Coimbra, Granada, Tübingen, München, Darmstadt, Graz, Paris) various scenarios (hadronic molecules, (multi-)quark states, hybrids) with all existing data (and eventually proposing new measurements). Systematic studies of charmonium states supplemented with lattice QCD investigations promise to give insight into the mechanism of quark confinement and the transition from strong (nonperturbative) to perturbative QCD (Murcia).

3.      Hadrons in nuclei. When hadrons are embedded in nuclei, their structure and dynamics can be investigated in a variety of different ways as compared to free space. For example, the characteristics of hypernuclei are very sensitive to the fundamental hyperon-nucleon and hyperon-hyperon interactions, and thus offer a fine laboratory to study these (Jülich, Granada, Barcelona). This venue will be pursued e.g. at J-PARC and FAIR. Furthermore, precision calculations in few-nucleon systems have become available that are sensitive to the small effects of isospin violation generated through the light quark mass difference m_u – m_d . Such effects will be studied in processes like dd → α π⁰ with a direct link to the experimental efforts of WASA-at-COSY (Jülich, Krakow, Manchester, Lisbon). A central issue for FAIR will be the interaction of D-mesons with nucleons to study charmed nuclei (Valencia, Granada, Barcelona, Darmstadt). First models of this hitherto unexplored reaction will be developed based on meson-exchange phenomenology and quark exchange effects (Valencia, Giessen, Mainz). Another central issue will be to further sharpen our understanding of possible medium modifications of hadrons in nuclei (Valencia, Giessen), such studies will also be extended to the properties of charmed hadrons. Another tool to investigate fundamental properties of QCD are hadronic atoms, i.e. Coulomb bound states subject to small QCD corrections. Here, work will focus on the theory of kaonic deuterium to prepare the analysis of the SIDDHARTA experiment at DAPHNE. Related to this are the investigations of three-hadron states, triggered by claims of the existence of deeply bound kaon-multi-proton clusters (Barcelona, Bonn, Valencia).

4.      EFT methods for continuum and discrete QCD. Finally, related to the aforementioned physics topics but also to guide and supplement lattice gauge simulations, EFT methods for continuum and discrete QCD will be further developed. Examples are chiral extrapolations for hadron properties (Bonn, Madrid, München, Lund, Bochum) and interactions (Barcelona) as well as the extraction of hadron resonance parameters from finite volume effects (Bonn, Bern, Marseille). Furthermore, work will be done (Pavia, Madrid, Murcia. Helsinki, Bern, Paris) on the combination of chiral perturbation theory and dispersion relations, which has already been proven to be a high precision tool for pion physics (as exemplified by the Roy equation analysis combined with chiral constraints that led to a one percent prediction of the pion-pion scattering lengths). Unitary extensions of CPHT and the properties of resonances in large N_c QCD will also be considered (Madrid, Murcia, Marseille). These methods constitute indispensable tools to understand the spectrum of QCD. Last but not least, renormalization group methods in hadronic systems will be studied and applied to hadron properties as well as nuclear forces (Coimbra, Manchester, Mainz). One example is the calculation of the leading three-body force and the related Efimov effect in nuclear and atomic systems, which is a reflection of the universality of physical phenomena in systems with a large two-body scattering length.

 QCDnet will coordinate the work of about 100 tenured researchers, 50 post-docs and about 65 graduate students in addressing topical issues in hadron physics and produce scientific publications in international research journals. The extensive co-operation will allow to develop common computational algorithms and methods, leading to a more efficient use of software resources. Among the studies which support specific Research Infrastructures and facilities are:

With the formal start of the large-scale FAIR project at GSI Darmstadt on November 7, 2007, new and challenging opportunities in hadron physics will emerge. A special emphasis is put on preparing the ground for an optimal physics output from the HESR at FAIR. This coordinated effort will train the young researchers who will have primary responsibility for exploiting the future facilities.

The expected synergetical effects from merging and relating the various approaches cannot be underestimated. Most of the groups that form the core of this theory network have already been working together on a more or less regular basis over many years in certain well defined subfields. A major aim of this network activity is to extend these borders considerably and strengthen the mutual interactions between all groups involved. QCDnet will be very closely tied to the experimental efforts in the field. The theoretical investigations within this network are required for the evaluation and interpretation of the existing data as well as for proposing new experiments and technologies at the various accelerators and laboratories.

The community of European hadron physicists has very strongly endorsed this proposal. It will constitute a truly outstanding European collaboration and as such be a model role for the whole European scientific community.